Individuals who undergo total knee arthroplasty for end-stage osteoarthritis report significant reductions in pain following surgery; however, their lower extremity functional abilities remain impaired when compared to healthy control subjects. Previous work from our lab has shown that the functional impairments are associated with maximal isomeric knee extension strength. However, during functional tasks, such as walking, rising from a chair, or climbing stairs, it is not only the strength of the involved musculature that determines performance, but the ability to generate the necessary muscle forces while the joint segments are in motion. Therefore, examination of quadriceps muscle power, the product of joint torque and movement velocity, may provide additional insight into the functional impairments those patients who undergo total knee arthroplasty exhibit. The current proposal is aimed at determining if patients who undergo unilateral total knee arthroplasty have deficits in knee extensor power and to examine the associations between knee extensor power capacity and lower extremity functional ability. By separately controlling for speed (isokinetic) and resistance (isotonic) during knee extensor contractions, we will be able to identify the rate limiting factor in power generation for patients recovering from total knee arthroplasty. We hypothesize that patients who undergo total knee arthroplasty will have lower peak knee extension power compared to age and sex matched healthy control subjects. We also hypothesize that knee extensor power will be significantly associated with performance in lower extremity functional activities. Specific Aim 1: Using a KinCOM electromechanical dynamometer, I first plan to determine if peak knee extensor power, measured isokinetically across a range of velocities and isotonically across a range of relative loads, differs between patients after total knee arthroplasty and healthy age and sex matched controls. Specific Aim 2: Using clinical tests of lower extremity functional ability, power outcomes during the isokinetic and isotonic contractions and standard motion analysis techniques of walking, rising from a chair and stepping, I plan to examine the associations between knee extensor power production and performance outcomes of functional tasks. Specific Aim 3: Through patient recruitment from the local hospital (standard of care) and patients treated in our outpatient rehab (progressive strength training), I plan to compare the changes in knee extensor power in response to different post surgical rehabilitation. Analyses of knee extensor power during functional and experimental tests in both patients and healthy controls will help identify the factors that limit full recovery of functional ability following total knee arthroplasty.